Good site for comparing prescription costs

A friend told me about GoodRx. I haven't played around with it much, because we are super fortunate to have Masshealth, but the site works, and various interwebs reviews tell me the information is accurate. Apparently the out-of-pocket cost for various meds can be a few dollars at one pharmacy chain and a few hundred at another. So definitely check it out before paying if you're ever told something isn't covered.